1. Field of the Invention
This invention relates to audio systems of the kind used in commercial and other large structures and more particularly to such a voice evacuation system readily adapted for multiple additional uses such as paging, background music etc.
2. Brief Description of the Prior Art
In voice evacuation systems, it is important to provide for continuous monitoring to insure the system is at all times in operating condition. Such monitoring requires continual testing of the amplifiers in the system and a supervisory alarm system to maintain a continuing check on the condition of the distribution circuits.
In the usual system, the output from a conventional audio amplifier is connected to a distribution circuit that includes a number of loudspeakers appropriately positioned to disseminate the desired instructions in the event of an emergency. One or more back-up amplifiers are provided and are arranged to be substituted for the main amplifier in the event of its failure.
To be certain of the proper functioning of th amplifiers, it is necessary to operate the amplifiers continuously, even when no emergency is present. It is also important to be certain of the operation during a power outage when the amplifiers must be operated from a back-up power supply. Because of the heavy power drain of the amplifiers during this period, large and expensive battery supplies are usually required.
In the event of failure of the main power amplifier, relay circuits substitute a back-up amplifier. This requires that each back-up amplifier have power capabilities equal to that of the main amplifier.
To supervise the operation of the distribution circuit, it is usual to disconnect the distribution circuits from the amplifiers and connect a monitoring voltage to the distribution circuit. An alarm is sounded if the distribution circuits are either open or short-circuited. Because of the limitations of the signal coupling, a direct monitoring voltage cannot be superimposed on the distribution circuit. The result is that the supervisory circuit is inoperative when the amplifiers are connected to the distribution circuits. This is a substantial difficulty because the most critical time for determining the proper operation of the distribution circuits is during an actual emergency.
This same limitation makes it necessary for any emergency lighting, signaling or control system, such as a series of lights, audible devices or other auxiliary controls, to be handled by a separate circuit.